The present invention relates in general to semiconductor devices and, more particularly, to low voltage integrated voltage regulators for supplying high transient output currents.
Personal computers currently are using microprocessors that operate with low power supply voltages while generating high transient switching currents. For example, typical microprocessors are specified to operate with supply voltages as low as 1.5 volts and narrow operating ranges while producing transient currents of at least thirty amperes.
The supply voltages often are generated by power supplies configured as voltage converters that include pulse width modulated switching regulators to conserve power. A typical switching regulator switches current through a coil to store energy on one portion of a cycle and then transfer the energy to a large output capacitor on another portion of the cycle to develop the supply voltage. However, switching regulators suffer from a low bandwidth, and consequently are unable to maintain the supply voltage within the specified range during a large load current transient. A high performance switching regulator has a bandwidth of about one hundred kilohertz, whereas at least one megahertz is needed for adequate regulation during a load current transient.
Power supplies can increase bandwidth by using Page 2 multiple switching regulators with parallel outputs and operating on staggered phases. However, multiple switching regulators do not improve the transient response enough to meet the requirements of current and future computer systems. Moreover, multiple switching regulators add substantially to the cost of the power supplies and the area occupied on a circuit board.
Hence, there is a need for a low voltage regulator that has a high bandwidth in order to maintain regulation of an output voltage during a large current transient.